The present technique relates to apparatus and methods for testing imaging devices. More particularly, the present technique relates to a phantom for testing imaging devices.
Medical imaging devices, such as X-ray systems, are omnipresent in modem medical facilities. Through the use of medical imaging devices, medical professionals, such as physicians, can produce detailed images of internal tissues, anatomies and organs of patients, thereby mitigating the need for invasive exploratory procedures and providing valuable tools for identifying and diagnosing disease and for verifying wellness.
Digital X-ray systems are becoming increasingly widespread for producing digital data that may be reconstructed into useful radiographic images. In traditional digital X-ray systems, a uniform beam of X-ray radiation is directed towards an object. As the beam passes through the object, materials of differing X-ray absorption and dispersion attenuate portions of the beam. Upon exiting the object, the attenuated X-ray beam impacts a detector, which measures the attenuation via photodiodes and transistors arranged in a matrix defining discrete picture elements or pixels of image data. By measuring this attenuation, the system may produce a radiographic image or projection of the object based upon the image data collected and processed. Advantageously, by analyzing the radiographic image, the physician may diagnose conditions of the patient.
Of particular note, digital subtraction angiography (DSA) procedures typically employ digital X-ray systems. To perform a DSA procedure, a medical professional may intravenously inject a contrast agent (e.g., a radiographically opaque substance, such as barium or iodine) into the patient to enhance the attenuation of the vasculature of the patient and provide desired contrast in the reconstructed X-ray image. That is, the medical professional may take a first image of the patient, without the contrast agent. This first image is generally known as a mask image. The medical professional may then intravenously inject the contrast agent into the patient. A second image of the patient is then taken. During typical DSA procedures, the patient must remain quite still to avoid artifacts and to improve the comparability of the resulting images. By subtracting the first image from the second image, primarily regions in which the newly injected contrast agent resides will remain visible in a difference or subtraction image. That is, the common elements of the two images are removed, leaving the newly injected contrast agent in the second image. Because the contrast agent flows within the circulatory system of the patient, the arteries and veins through which the contrast agent flows are highlighted.
Typically, the quality of the image produced by a digital X-ray system is defined by its contrast ability and by its resolution ability. In the medical industry, contrast ability refers to the extent to which the various different kinds of tissue within the body are displayed with respect to one another. That is, the discernability of one kind of tissue from another. Resolution, however, refers to the ability of the imaging device to reveal fine detail. That is, resolution typically refers to the ability to distinguish between small, closely spaced elements within the patient. By improving the contrast and resolution of a produced image, a physician, for example, may better diagnose a patient, because of the detail of the information provided by the image. Moreover, by gauging the abilities of the X-ray system, a physician may be able to determine whether the image is of sufficient detail to support a certain diagnosis. Higher resolution and contrast also aid in image enhancement processing on the collected image data in which features are filtered and otherwise clarified for analysis and viewing.
To improve the image produced and/or to gauge the capabilities of the imaging device, imaging devices are typically tested and/or calibrated. In certain instances, these testing and calibration procedures may employ phantoms. A phantom is generally an object of known physical characteristics that is placed in the system during test imaging sequences to determine how the system performs in one or more ways. Phantoms are typically used to measure system responses, adjust imaging parameters, qualify systems, calibrate systems, and so forth. The dimensions and composition of a phantom from which a test image is produced are known prior to the production of a test image. Thus, the test image of the phantom is compared with the known parameters of the phantom itself to reveal the accuracy and/or limitations of the imaging device. Accordingly, the imaging device may be recalibrated for maximum performance. Phantoms are typically designed based upon the physics of the particular type or modality of imaging system to be tested, and may be specifically designed for a particular type of image to be produced.
Typical phantoms, however, present a number of concerns. For example, traditional phantoms used to test for DSA procedures are relatively unwieldy items. That is, the technician may not be able to easily move such traditional phantoms from location to location. Moreover, traditional phantoms may not emulate human tissue ideally. For example, a traditional DSA phantom may be a substantially homogenous block of a clear plastic material. Accordingly, such construction may not accurately represent the diversity of tissue within the body. Moreover, in imaging procedures, such as DSA, inadvertent movement of the phantom may negatively impact the produced test image or images, i.e., the images used to generate the subtraction image.
Accordingly, there is a need for an improved technique for testing and gauging performance of imaging devices. Particularly, there is a need for a technique that reduces the difficultly and expense of servicing, repairing, calibrating and qualifying imaging devices, particularly those used for DSA imaging.